Question: William starts counting at 42, and he counts by fours. If 42 is the 1st number that William counts. what is the 15th number that he counts?
Answer: What is the first number that he counts? $42$ What is the second number that he counts? $\begin{align*}&42 + 4 \\ &= 46\end{align*}$ What is the third number that he counts? $\begin{align*}&42 + 4 + 4 \\ &= 42 + (2 \times 4) \\ &= 50\end{align*}$ What is the 15th number that he counts? $\begin{align*}&42 + (14\times4) \\ &= 42 + 56 \\ &= 98\end{align*}$